An HVDC power supply system is required for driving an electric machine that incorporates a high voltage electrical drive motor and electric auxiliaries. The integrity of the high voltage system is critical to the reliability and integrity of the machine. Typically, the machine frame is electrically insulated from the terminals or conductors of the high voltage power supply.
Under normal working conditions, DC leakage currents on the order of microamps exist between the conductors of the high voltage power supply and the machine frame. Thus, the leakage resistances between the conductors of the high voltage power supply and the frame are normally very high. However, under faulty conditions (e.g., insulation failure), electric currents from a high voltage power supply may leak to a machine frame. Such leakage currents, when significant, may be an indication of machine component fatigue or failure of a conductor's insulation. In order to ensure the proper operating conditions and the integrity of the machines, it is necessary to detect electrical leakage between the conductors of the high voltage power supply and the machine frame.
Further, the configuration of certain high voltage systems requires that the high voltage and low voltage conductors of the high voltage power supply are balanced in reference to the machine frame. For example, the conductors of a high voltage power supply in the system may be +100V and −100V when referenced to the machine frame. For this type of high voltage system configuration, it is desirable to compensate for unbalanced electrical leakage currents so that the system will stay balanced and centered in reference to the machine frame.
Conventional systems and methods have been implemented to detect electrical leakage. For example, U.S. Pat. No. 6,700,384 to Yugou (the '384 patent) discloses a power source device having a cell unit comprising a plurality of cells. In the '384 patent, a first current line having two voltage dividing resistors interposed therebetween is connected between a positive side terminal and a negative side terminal of the cell unit. A second current line having two protection resistors and two detection resistors interposed therebetween is also connected between a positive side terminal and a negative side terminal of the cell unit. An intermediate point of the second line is grounded via an insulation resistor. The voltage difference between a voltage (V1, V2) detected by the detection resistors and a reference voltage (Vc) obtained from a point of connection between the voltage dividing resistors is provided as the input to two Op-Amps serving as the input voltage (V1IN, V2IN). Based on the output voltage (V1OUT, V2OUT) obtained from the Op-Amps, leakage occurrence is detected.
While prior art systems, such as the '384 patent, may detect electrical leakage, they do not detect electrical leakage in a balanced fault condition. The disclosed embodiments improve upon these prior art systems by, in one embodiment, providing a compensation mechanism that automatically compensates for electrical leakage in a circuit so that the circuit stays balanced in reference to the machine frame. The disclosed embodiments further improve upon prior art systems by, in another embodiment, providing a leakage detection mechanism that detects electrical leakage in a circuit with balanced leakage resistance. Additionally, the disclosed embodiments improve upon the prior art systems by providing a faulty connection detection mechanism that can be used to detect a faulty ground strap connection in a machine.